The present invention concerns a charge-to-voltage converter. These are used, for example, in charge-transfer devices.
A charge-to-voltage converter comprises a read diode and a read amplifier. The diode has a diffusion capacitance Cd and the amplifier has a gain G. Professionals of the art will know that the characteristic parameter of a charge-to-voltage converter is its so-called conversion factor which relates the output voltage to the input charge.
The theoretical value of the conversion factor is FCC=G/Cd.
However, owing to the existence of parasitic capacitances acting in parallel with the diffusion capacitance Cd (overlapping capacitance Cr of the diode, and the Miller capacitance Cm fed back to the input of the amplifier), the conversion factor is more correctly given by the relation: EQU FCC=G/(Cd+Cr+Cm)
According to the prior art, the gain G is adjusted using a resistance R outside the component constituting the charge-transfer device. This resistance fixes the gain, the base width and the noise in the read chain, which includes, in addition to the charge-to-voltage converter, another amplifier followed by a low-pass filter, which in turn is followed by a double correlated sampling circuit.
Such a device has a number of disadvantages. In particular, owing to the poor gain of the conversion stage, the complete chain has non-optimized noise characteristics because most of the amplification is achieved after the read amplification. This problem becomes serious in applications involving processing of signals of low amplitude.
The present invention overcomes these problems.